Tracing table



Feb. s, 1955 w. s. LOESCH TRACING TABLE 2 Sheets-Sheet 1 Filed Aug. 8,1952 INVENTOR:

WZ/fliam )5. Zoesc/l ATTORNEY w. s. LOESCH TRACING TABLE Feb. 8, 1955 2Sheets-Sheet 2 Filed Aug. 8, 1952 24- INVENTIORI:

WWW/am ,8. ,loesc/z ZZ N ATT United States Patent TRACING TABLE WilliamS. Loesch, Vestal, N. Y.

Application August 8, 1952, Serial No. 303,448

3 Claims. (Cl. 240-2) This invention pertains to tracing tables, such asare used by artists, draftsmen and engineers for the tracing ofdrawings, prints, photographs and like materials. The invention dealsspecifically with an improved construction and arrangement of partswhich provides adequate and controlled illumination through the materialbeing copied, with a minimum of heat and low consumption of power. Otherfeatures of the invention include a simple and rugged mechanicalconstruction, the provision of a chamfered front construction for mostconvenient use, and centralized controls for selectively energizing thelamps employed.

It is well known to provide a drawing or tracing table with a clearglass panel which is illuminated from beneath in order to rendertransparent various materials placed thereon, so that the same may betraced on to paper or other surfaces. Prior designs of this type havenever met with much success, however, because their use has alwaysentailed complications. Thus, where incandescent electric lamps havebeen used as the light source, a considerable amount of heat is thrownup through the material being copied, and their use for protractedperiods has been either extremely uncomfortable or impossible. Attemptsto reduce this effect have been made, as by using only one or a fewlocalized light sources, such as incandescent lamps; however, to obtainadequate illumination at the particular locality in use, this hasinvolved complicated arrangements for the moving of the light or lightsfrom point to point. The use of enclosed cabinets has been suggested,but these either aggravate the heat problem or use so few lights, fixedor adjustable in position, that the illumination is inadequate.

Ideally, it would be desirable not only to vary the intensity of theillumination provided, but also to be able to control its spatialdistribution. The intensity control is desirable not only because of thevariations in opacity encountered in materials being copied, and thevariations in thickness and opacity of the paper being used, but alsobecause the visibility of the material depends to a considerable extentupon the general illumination in the work area. Thus, a rather faintillumination may be adequate where the surroundings are relatively dark,while a considerable brightness must be provided where the user isworking in strong light. The desirability of some position control ofthe light source springs from the fact that the sizes of the subjectsvary; quite often, also, only a portion of a large original print ordrawing is to be traced, and it is desirable to localize the greatestintensity at this portion.

The present invention has for its principal object the provision of atracing table arrangement providing a maximum of well-diffusedillumination over the desired work area, While at the same timesubstantially eliminating excessive heat. To this end, the inventionutilizes a comparatively large number of tubular light sources, such asfluorescent lamps, distributed beneath a transparent glass plate,together with switching means for enabling the user to energize either afew of the lamps located predominantly at one end of the transparentplate, or distributed more widely over its area. In this way, both theaverage intensity of lighting and its spatial distribution can becontrolled.

A subsidiary object of the invention is to ensure the adequate diffusionof the light transmitted through the material being traced, by meanswhich also serves as a heat insulating shield between the light sourcesand the working surface. To this end, a ground glass or other diffusingr45 ice plate is interposed in spaced relation between the upper glassplate and the light sources, thereby insulating the upper plate, whichforms the actual working surface, from the heat generated by the lightsources. Clearly, certain forms of spaced-panel glasses (such as used inwindow construction) may also be employed.

Still another object of the invention is to provide an arrangement ofthe above type in which ventilating openings are provided and sodistributed as to utilize the chimney effect to ensure an adequatecirculation of room air over the light sources and out of the boxforming the body of the device. In addition, the ballast units providedfor the fluorescent lamps are mounted outside the box itself, so thattheir heat dissipation does not contribute materially to the totalreaching the working surface.

The above and other objects and advantages of the invention will best beunderstood from the following detailed specification of a preferredembodiment thereof, given by way of example, and taken in connectionwith the appended drawing, in which:

Fig. l is a side elevation of the tracing table of the invention, withparts broken away and in section to illustrate the internalconstruction;

Fig. 2 is a front view of the device, again with parts broken away forclarity;

Fig. 3 is a fragmentary enlarged perspective view, partly broken away,of a front corner of the device; and

Fig. 4 is a wiring diagram showing one form of selective control for theplural light sources of the device.

Referring now to the drawings, and especially to Figs. 1 and 2 thereof,a preferred embodiment of the invention is shown as comprising a tracingtable generally designated by the numeral 10, and comprising a shallowbox having walls formed of any suitable material, such as wood or metal,and provided with an upper panel frame 12 having a central aperturewithin which is mounted a panel 14 of clear plate glass or plasticmaterial, the latter being supported within the aperture as by rabbetsor rails about the edge of the aperture. Beneath this aperture occupiedby transparent panel 14, and surrounding the same, is a subordinateframe 16 rabetted or grooved to receive a sheet or plate 18 of diffusingmaterial, preferably ground glass or opal glass. As shown in Fig. l, theunderside of the top panel frame 12 may have secured thereto the spacingblocks such as 20, which operate to fix the position of the entire topassembly with respect to the shallow box containing the light sources tobe described. The presence of these spacers or locators enables the topassembly to lie securely in place upon the top of the box without fixedfasteners, so that it may readily be removed, for example for thepurpose of replacing light sources, or for other purposes.

The bottom wall of the shallow light box, designated by numeral 22,supports on its inner surface a plurality of parallel, spaced-apartlight sources 24, which are preferably of the instant-startingfluorescent type having elongated tubular form. These extend across andbeneath the area of the glass panel 14 and glass plate 18, so as to casttheir light therethrough and through any materials placed upon the upperpanel 14. As shown in the drawings, there may be a considerable numberof these sources, ten being shown by Way of illustration, and they arefixed in position. While fluorescent lamps have been stated as thepreferred light source, because of their relative coolness of operationand the diffuse nature of their light, other equivalent sources may ofcourse be used; also, the fluorescent lamps need not necessarily be ofthe instantstart type, although the latter are more convenient to usesince they permit rapid changes in the lighting combinations by themeans to be described below.

As shown in Fig. 2, and especially in the perspective view of Fig. 3,the sockets 26 for the tubular lamps 24 may be mounted upon metalconduit strips 28 extending along both lateral edges of the interior ofthe box. The depth of the box itself is such that the lamps 24 arespaced somewhat below the diffusing plate 18, as this contributes touniformly of the illumination transmitted to the upper clear glass panel14. The interior of the box itself is preferably painted or otherwisecoated with a reflecting and/or diflusing material, such as aluminumpaint, or porcelain-enameled reflectors, or the like may be employed,which will contribute appreciably both to the amount of light reflectedthrough the upper panel 14 and to its uniformity.

It will be observed that the spacebetween the upper clear glass panel 14and the lower diffusing plate 18 is a dead-air space, in that it isclosed off from direct communication with the portion of the boxcontaining the light sources 24. Thus, advantage is taken of the spacingdesired between these plates (for optical reasons of light diffusion) toprovide a shield against the transmission of heat to the working surfaceof the device by convection currents.

In order to provide the desired spacing distance between the upper panel14, difiusing plate 18 and light sources 24, plus the distance requiredfor the mounting of the latter, a thickness dimension for the box is required which makes it rather unhandy for the user, who normally sitswith the front edge of the box approximately in his lap. A thickness ofabout 8 inches is the smallest which can be used and provide thenecessary structural features, while a thickness of not over 6 inches isabout the maximum that can be tolerated at the front of the device forcomfort. The present invention therefore provides the structure bestshown in Figs. 1 and 3, in which the bottom surface of the box istapered to provide the desired dimension at its front end. Thus, thefront of the box is formed by a panl 30 perpendicular to the top panelframe 12, and connected to the bottom 22 of the box by the inclinedpanel 34, which will be approximately parallel to the user's lap whenthe device is tilted to a comfortable working position. In thisconnection, it may be mentioned that while the tracing light box of theinvention is capable of use without legs, especially in the smallersizes, being supported for example by an ordinary table, it can equallywell be provided with a support of its own, preferably one which permitsthe height and inclination of the box to be adjusted. Such a supportcomprising legs 36 is indicated by chain lines in Fig. 1, so illustratedbecause it does not form an essential part of the present inventionitself; the support structure may obviously be provided with height(rack-and-pinion) and inclination adjustments.

In order to decrease further the quantity of heat which is directedtoward the working surface of the device, advantage is taken of thechimney eflect resulting from the normal inclination of the device, andthe heat generated by the lamps 24. To this end, the front inclinedpanel 34 is provided with a plurality of ventilating openings 38, andthe rear wall 40 of the box (Fig. l) is provided with similar openings42. As illustrated by the flow arrows in Fig. 3, air heated by the lamps24 will rise toward the rear of the boxfor egress through openings 42,and cool room air will be induced to enter via front openings 38. Theair flow will withdraw heat from the lamps 24 that might otherwise findits way through the clear glass plate 14, and the flow of air over theunder surface of the diffusing plate 18 will also tend to wipe thissurface and keep it cooler than would otherwise be the case.

The use of the desired fluorescent lamps in the present inventioninvolves the use of the inductive auxiliaries normally required fortheir operation, known as ballasts. These devices in themselvesdissipate a material quantity of heat, and it is desirable to locatethem as far as possible from direct communication with the workingsurface of the device. As shown in Figs. 1 and 2, it is preferred tomount these devices, as indicated at numeral 44, on the outside of thebottom panel 32 and nearer the rear of the box than the front. Thislocation places these heat-dissipating elements completely outside thebox, and away from the working surface. Smaller, portable models of thetracing tables, that could be set on a table top or desk, could have theballast support brackets combined with rear legs or elevators t inclinethe working surface to facilitate easier use by the draftsmen. Such rearlegs are indicated in Fig. l at 52.

Reference has been made to the use of a substantial number of tubularlight sources in fixed positions within the box, and to the advantagewhich results from control of the lighting intensity and locationpattern. The present invention achieves this result by providing forindependent. control of the energization of groupsof the lamps 24, butby simple and convenient means. As shown in Figs. 1 to 3, the controlcomprises a group of three switches located in ganged relationshipadjacent the front of the right-side panel of the box. Switches A and B'may be ordinary single-pole toggle switches, while the third switch maybe an ordinary double-pole toggle switch having blades C and C.

As best shown in the schematic wiring diagram of Fig. 4, the lamps 24and ballasts 44 (of which five are required in the disclosed embodiment,each energizing two of the ten lamps shown) are so connected that theswitches permit not only complete on-off control for all lamps, but alsoa degree of selectivity of energization of different pairs of lamps. Inother embodiments, each lamp may have its own ballast, withcorresponding circuit changes. The lamps in Fig. 4 are designated bysuperscripts, such as 24 24 and so on, the superscript indicating theposition of the lamp counting from the front edge of the device.Terminal strips or blocks 46, 43 are provided to facilitate connections,and the wiring is arranged so that the following lamp combinationscorrespond to operation of the switches:

Switch combination Lamps energized All open none. A only closed. 24 and24 It will be seen that the closing of switch A lights lamps 24 and 2.4which provides illumination of moderate in tensity for substantiallyhalf the working surface, and provides for working on relatively smallobjects of lesser opacity. Closing of switches A and CC lights lamps 2424 24 and 24 providing full intensity for substantially half the workingsurface and permits working on the smaller objects having greateropacity. Closing switches A and B lights lamps 24 24 24 and 24 whichprovides moderate intensity for the full working surface. Closure of allthree switches provides the maximum amount of light distributeduniformly over the working area. With this arrangement, not only is thelighting under adequate control, but the amount of heat generated can beminimized where only a moderate amount of light is required. The usualconnection plug is provided to enable the device to be powered fromstandard outlets.

While the invention has been described herein in considerable detail byway of example, it is obvious that numerous changes in structure andarrangement can be made by those skilled in the art without departingfrom the spirit of the invention, and the invention is therefore notto'be understood as limited to such details, but only by the scope ofthe appended claims.

I claim:

1. A tracing table comprising a relatively shallow opaque box structurehaving side walls, front and back walls and a bottom panel, a cleartransparent panel mounted substantially flush with the upper surface ofsaid structure, an obliquely disposed panel running from side wall toopposite side wall and connecting the bottom panel with said front wallto provide a chamfered lower front edge adapting the structure to use ina position inclined to the horizontal, a plurality of tubular lampsdisposed beneath said transparent panel and all parallel to said frontwall, an energizing circuit for said lamps, and a group of switches eachconnected in said circuit and respectively connected to selected groupsof said lamps, one of said switches controlling certain only of thelamps nearer the front wall, a second switch fed through the firstswitch and controlling certain of the lamps located more remote from thefront wall, and a third switch having two circuits fed respectivelythrough the first and second switches, one circuit controllingadditional of the lamps nearer the front wall and the other circuitcontrolling lamps distributed both forwardly and rearwardly of thepanel, whereby a relatively small number of switches can controllighting combinations distributed both as to the general area of thetransparent'panel and as to the degree of illumination in the forwardarea thereof.

2. The invention in accordance with claim 1, in which said lamps arefluorescent lamps, and including ballast elements electrically connectedto said lamps and dis- References Cited in the file of this patentUNITED STATES PATENTS 1,348,957 Pope Aug. 10, 1920 6 Smith et a1. June8, 1926 Mason Oct. 10, 1933 Cadenas Feb. 17, 1948 Long Aug. 9, 1949Hoffman Sept. 11, 1951 Winkler et al Aug. 12, 1952 FOREIGN PATENTSGermany Oct. 19, 1920 Austria July 25, 1924 Great Britain Apr. 29, 1931

